Stretch marks are narrow streaks or lines that occur on the surface of the skin.
Doctors often refer to stretch marks as stria, striae or – during pregnancy – striae gravidarum.
Stretch marks are often red or purple to start with, before gradually fading to a silvery-white colour. They're usually long and thin.
Where stretch marks occur
Stretch marks can occur anywhere where the skin has been stretched, but they usually affect areas where fat is stored, such as the:
shoulders (in bodybuilders)
Sometimes, particularly in teenage boys, stretch marks can develop on the back, overlying the spine horizontally (like the rungs on a ladder).
Stretch marks caused by Cushing's syndrome (where the blood contains high levels of a hormone called cortisol, see below) tend to be wider and larger, and can also appear on the face.
When stretch marks occur
Stretch marks often occur:
after rapid weight gain
if you have a family history of stretch marks
if you have an underlying health condition or a syndrome, such as Cushing's syndrome or Marfan syndrome
after the prolonged or inappropriate use of corticosteroid medication
Stretch marks often occur during the later stages of pregnancy, affecting about eight out of 10 pregnant women. Whether or not you'll get stretch marks depends on your skin type and how elastic it is.
During pregnancy, hormones are produced that soften the ligaments in your pelvis so they're more flexible when you give birth. Ligaments are strong bands of tissue that connect joints. However, the hormones also soften the fibres in your skin, making it prone to stretch marks.
As your baby grows and your skin stretches, you may get stretch marks on your tummy. You may also develop them on your thighs and breasts as they get bigger.
Stretch marks usually fade and become less noticeable after childbirth, but they don't always disappear completely.
Rapid weight gain
You may get stretch marks if you put on a lot of weight over a short period of time. They sometimes remain even after losing weight, but should eventually fade.
Regular dieting can cause stretch marks as your weight goes up and down. If you need to lose weight, lose it slowly and steadily so that your skin isn't put under strain. Read more about how to lose weight safely.
Bodybuilders and athletes can also get stretch marks as their muscles increase in size.
During puberty, the body often develops very quickly in growth spurts.
Boys may get stretch marks on their shoulders and back, and girls may get them on their hips, thighs and breasts.
If you have a close relative with stretch marks, such as your mother, you're more likely to develop them yourself.
Although stretch marks can affect both male and female family members, they're more common in women.
Underlying health conditions
Stretch marks can sometimes be related to rare conditions or syndromes, such as Cushing's syndrome and Marfan syndrome.
Cushing's syndrome occurs when the body overproduces the hormone cortisol, which is thought to cause stretch marks.
Marfan syndrome is caused by a faulty gene that weakens the body's skin and connective tissues, reducing their elasticity (ability to stretch). This means the skin isn't as resistant to stretch marks as it should be.
Treating stretch marks
Most stretch marks aren't particularly noticeable and will fade over time.
If you have unsightly stretch marks, or if they affect a large area of your body, there are a few treatment options available. However, there isn't much evidence to show that these treatments work.
Cosmetic camouflage (make-up) is available over-the-counter at pharmacies. It can be used for small areas of skin affected by stretch marks. Some types are waterproof and can last two to three days.
Creams, gels and lotions
The manufacturers of creams, gels and lotions often claim that they can remove stretch marks. However, it's unlikely they can prevent stretch marks occurring, or make them fade any more than they will over time.
These products are essentially skin moisturisers and are available from pharmacies, supermarkets, and health and beauty shops. They should usually be applied when your stretch marks are still red or purple.
Laser therapy can't completely remove stretch marks, but it may help fade them and make them less noticeable.
Several different types of laser therapy are used to treat stretch marks.
Pulsed dye laser treatment is one type of laser treatment available. It's painless and can be used at an early stage, while your stretch marks are still red or purple.
The energy from the laser is absorbed by the blood vessels underneath your stretch marks. The blood vessels collapse and the red or purple colour either disappears completely or turns white.
Cosmetic surgery for stretch marks is expensive and rarely recommended.
If you have stretch marks on your abdomen and a large amount of loose skin, it may be possible to have an abdominoplasty (tummy tuck).
This is a type of cosmetic surgery that removes excess fat and skin from your abdomen, and also gets rid of stretch marks below your belly button.
Preventing stretch marks
Stretch marks can't always be prevented – for example, they often occur during pregnancy. However, there are some things you can do to help lower your chances of getting stretch marks.
Weight and diet
Stretch marks are often caused by gaining weight rapidly over a short period of time. Avoiding rapid weight gain and weight loss ("yo-yo dieting") can help prevent stretch marks.
If you need to lose weight, you should do it slowly by eating a healthy, balanced diet and exercising regularly. You shouldn't lose more than 0.5kg (1lb) a week. Read more about how to lose weight safely.
It's important to eat a healthy, balanced diet that's rich in vitamins and minerals, particularly vitamin E, vitamin C, and the minerals zinc and silicon. These vitamins and minerals will help keep your skin healthy.
A balanced diet will provide all the vitamins and minerals your body needs. Dietary supplements aren't needed to prevent stretch marks.
Body mass index (BMI) is a measure most people can use to check whether their weight is healthy in relation to their height and build. For most adults, a BMI of 18.5 to 25 is considered healthy.
In Marfan syndrome, stretch marks can occur on the shoulders, hips and lower back.